The present invention relates to a method and device for reducing electric field concentrations in electrical components.
In order to completely isolate components in integrated circuit from each other trench techniques may be used in a silicon-on-insulator (SOI) material. The SOI material which the component is to be formed on may consist of a thin layer of silicon on an insulating material. The component is completely isolated from the surroundings by a trench being etched down to the isolating substrate around the circumference of the component to be isolated. An isolating material, which can differ from that of the insulating substrate, is then deposited in the trench. This leaves components in the form of an island of silicon surrounded by insulating materials--laterally by the filled trench of isolating material and vertically by the insulating substrate
The insulating substrate and the trench isolating material could be, for example, silicon oxide, silicon nitride, sapphire, aluminium oxide or the like. Trench techniques and SOI technology are know from SZE, S.M., "VLSI Technology--2nd edition" 1988, McGraw-Hill Book Company, New York, USA and from SORIN CRISTOLOVEANU and SHENG SLI "Electrical Characterisation of Silicon-On-Insulator Materials and Devices" 1995, Kiuwer Academic Publishers, Massachusetts, USA.
This technique can be used to isolate high voltage components. However problems can occur owing to the electric field being concentrated at the sharp corner region of the active component. This electric-field concentration reduces the avalanche breakdown voltage of the corner region and this part of the device tums on at a lower voltage than the interior portion of the device. This problem is exacerbated in the case that a conductor with a high-voltage crosses the trench. This can lead to a lower than expected avalanche breakdown where the high-voltage conductor crosses the regions in which the electric-field concentration is highest.